1. Field of the Invention
The present invention concerns a microwave location system.
2. Description of the Prior Art
French patent No 2 608 119 discloses a railroad vehicle location system comprising a hollow tube parallel to the track forming a waveguide of which an emissive surface comprises an array of apertures through which microwave radiation passes, a unit for feeding microwave radiation into said hollow tube and a microwave receive antenna on board the railroad vehicle located near the side of the tube comprising the array of apertures which is adapted to enable the transmission between said apertures and said antenna of two distinct electric field signals.
To be more precise, to enable absolute location of the vehicle some apertures in the emissive surface of the hollow tube are perpendicular to the axis of the tube and some others are oblique to this axis, arranged in a particular pattern representing an appropriate code, the apertures perpendicular to the axis transmitting an axial component and the apertures oblique to the axis further transmitting a perpendicular component.
This document teaches also a method of transmitting data between a railroad vehicle and a traffic control station and simultaneously determining the relative location of the vehicle which entails choosing for the waveguide microwave feed unit an emitter of two different microwave frequencies, one dedicated to data transmission and producing a constant amplitude of the electric field signal received by a receive antenna on board the vehicle and the other dedicated to location and producing significant amplitude fluctuation in the electric field signal received by a location antenna also on board the vehicle to enable the speed of the vehicle to be measured by counting the number of apertures and therefore its relative location to be determined.
An object of the present invention is to provide a microwave location system which, in one configuration at least, requires only one electric field signal to be radiated to determine the absolute location of a mobile element, although this does not rule out the system being used also to determine the relative location of said mobile element or extending said configuration to transmit also an electric field signal, for example to have the system implement additional functions separate from the location function itself such as transmission of data to or from said mobile element, measuring the speed of said mobile element, etc, or, in the case where said radiation is produced by means of a certain number of radiating slots in the waveguide, providing certain embodiments of this location system.